One key factor in MOSFETS of whatever gate threshold that are being used
as on-off switches is that if it was possible to switch the gate drive
instantaneously, the dissipation is almost 100% due to the intrinsic
impedance of the silicon itself -- very low! Thus low heating at very hogh
currents. The gate drive current is almost zero AFTER the associated FET
and circuit capacitance has been charged or discharged.
Ralp
On Sat, 28 Jun 2003, Bryan Andersen wrote:
> The word as I have it from a chip designer is that logic level MOSFETs
> actually don't saturate untill they get to the normal MOSFET voltage
> around 10V. It is just that thay have crossed a threshold where
> additional voltage gains very little in saturation so their Rds on drops
> very little from 5V to 10V. At this point I just look for the part that
> will handle the current and voltage I want that also has the lowest Rds
> on. Then give it a high current gate drive circuit so it stays in the
> ON/OFF transition zone as short as possible. Propper decoupling of the
> gate drive chip is a must.
>> - Bryan
>>rten at new.metronet.com wrote:
> > EXCEPT that I have some new 9v alkaline cells here that measure 9,4 - 9.5
> > volts. Even so, as I noted in a previous post, logic level
> > enhancement-mode MOSFETs will saturate with 5v drive. The circuitry as
> > drawn is valid, given that n-channel devices are used.
> > Ralph
>> > On Thu, 26 Jun 2003, Chuck McManis wrote:
> >>At 10:16 PM 6/26/2003 -0500, rten at new.metronet.com wrote:
> >>>I noted a 10v. battery shown. I am not aware of a cell technology that
> >>>produces that vo9ltage????
>> >>:-) You're right of course, but if I drew a "voltage source" Ted might have
> >>become totally lost. Given the lack of current needed to switch the gate a
> >>9V alkaline's open circuit voltage might be near 10V :-)
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